If a vehicle is involved in a rear impact, for example the vehicle is struck from behind, the chassis of the vehicle is given a very sudden forward acceleration. The squab of a seat mounted in the vehicle and also the back rest of the seat will, consequently, move with a very swift acceleration, thus imparting the same acceleration to the buttocks and torso of an occupant of the seat.
However the head of the occupant, which has a substantial mass, is not contacted by any part of the seat and will thus remain stationary. Consequently the thorax of the seat occupant will move forwardly, whilst the head remains stationary, initially distorting the neck of the seat occupant. Subsequently, an acceleration will be imparted to the head of the occupant, by the occupant's neck, the acceleration initially being a rotational acceleration about the centre of gravity of the head, and subsequently being a forward acceleration that will accelerate the entire head of the seat occupant forward. This may impart substantial stress to the neck of the seat occupant giving rise to so called “whiplash” injuries.
Various proposals have been made to provide a headrest which, in response to a rear impact, moves forward so as to engage the rear part of the head of the seat occupant. Provided that the headrest moves forward sufficiently early during a rear impact situation, the head of the occupant may be engaged in such a way that it is given an acceleration which is virtually identical to the acceleration imparted to the buttocks and thorax of the seat occupant. In this way the head of the occupant will move almost simultaneously with the torso, and thus only a minimum distortion of the neck will occur, thereby reducing the likelihood of serious “whiplash” injuries.
It has been proposed to provide a headrest on a vehicle seat, the headrest being pivotally mounted in position and being associated with a pressure plate located in the backrest of the seat, so that if the torso of the seat occupant is driven rearwardly into the backrest, the pressure plate moves rearwardly causing the pivotally mounted headrest to move forwardly into engagement with the back of the head of the seat occupant.
Typically such prior arrangements are relatively complex, and, in many cases a pivot bearing is provided.
In view of the above, it is apparent that there exists a need for an improved vehicle seat.